Spinel compound has been demonstrated to be a most promising cathode material for lithium ion batteries among these candidates, e.g., LiCoO.sub.2, LiNiO.sub.2, and Li.sub.x Mn.sub.2 O.sub.4, since Li.sub.x Mn.sub.2 O.sub.4 offers several advantages in term of low cost, easy preparation and no toxicity. The common preparation method was first described by Hunter. The compound was prepared from a solid state reaction of LiCO.sub.3 and Mn.sub.2 O.sub.3 or Mn.sub.3 O.sub.4 in the Li/Mn molar ratio of 1/2 in air at 600.degree.-650.degree. C., followed by heating it at 800.degree.-900.degree. C. in air. However, the resulting compounds prepared by this method exhibited low capacity and poor reversibility. A marked improvement in preparation of spinel Li.sub.x Mn.sub.2 O.sub.4 with a large capacity was achieved by reacting stoichiometric amounts of Li.sub.2 CO.sub.3 and MnO.sub.2 in air with three consecutive annealing steps at 800.degree. C. (each for 24 h), and then further grinding to obtained spinel with the particles of about 1-2 .mu.m (U.S. Pat. No. 5,192,629). Although this technique can be carried out in air, it is too complex to apply for industrial production. More recently, a simple and cheap process route for synthesizing a spinel Li--Mn--C) compound was of a melt-impregnation method suggested by M. Yoshio. This involved a direct synthesis by a reaction of LiNO.sub.3 or LiOH with MnO.sub.2. One of the advantages of the compounds produced by this method is application of a lower final heating temperature, which will cause rather higher surface area of the resulting compounds. However, LiNO.sub.3 easily adsorbs water, thus is difficult to control the required composition of Li/Mn, also the gas NO.sub.x produced will pollute the environment. LiOH will adsorb the CO.sub.2 in air. From a manufacturing viewpoint, it is unlikely that LiNO.sub.3 (cost, toxic emission) or LiOH (cost, reaction with CO.sub.2) are viable candidates for LiMn.sub.2 O.sub.4 preparations. It would be welcome to develop a cheap and easy synthesis to produce the spinel electrode material in industrial scale using Li.sub.2 CO.sub.3 as lithium source.